Human hypertension represents a disease of multiple etiologies. Included among these is a sodium and volume dependent low renin form of hypertension. Drugs that act to control one aspect of hypertension will not necessarily be effective in controlling another.
Enkephalin, a natural opiate receptor agonist, is known to produce analgesia, and it is also known that enkephalin is inactivated by a neutral metalopeptidase (EC 3.4.24.11) frequency referred to as enkephalinase or enkephalinase A. Various NMEP inhibitors have been discovered which, by their inhibition of this enzyme elicit an analgesic effect. To date, no significant cardiovascular activity has been attributed to NMEP inhibitors. The NMEP inhibitor thiorphan was found to inhibit peripheral ACE, but to have little direct cardiovascular activity in its own right: blood pressure and heart rate were not affected. See T. Baum, et al, "Enkephalinase A Inhibition by Thiorphan: Central and Peripheral Cardiovascular Effects", Eur. J. Pharm., 94(1983), pg 85-91.
One class of drugs which is known to be effective in treating some types of hypertension is angiotensin converting enzyme (ACE) inhibitors, which compounds are useful in blocking the rise in blood pressure caused by increases in vascular resistance and fluid volume due to the formation of angiotensin II from angiotensin I. For a review of ACE inhibitors, see M. Wyvratt and A. Patchett, "Recent Developments in the Design of Angiotensin Converting Enzyme Inhibitors" in Med. Res. Rev. Vol. 5, No. 4 (1985) pp. 483-531, incorporated herein by reference.
It has recently been discovered that the heart secretes a series of peptide hormones called atrial natriuretic factors (ANF) which help to regulate blood pressure, blood volume and the excretion of water, sodium and potassium. ANF were found to produce a short-term reduction in blood pressure and to be useful in the treatment of congestive heart failure. See P. Needleman et al, "Atriopeptin: A Cardiac Hormone Intimately Involved in Fluid, Electrolyte and Blood-Pressure Homeostasis", N. Engl. J. Med., 314, 13 (1986) pp. 828-834, and M. Cantin et al in "The Heart as an Endocrine Gland", Scientific American, 254 (1986) pg. 76-81.